1. Field of the Invention
This invention relates to thin-film heads which are used for the perpendicular magnetic recording and reproduction of data or information in a computer, tape or videotape recorder, or like apparatus.
2. Description of the Prior Art
The magnetic recording and reproduction of data or information from a recording medium, such as a floppy or rigid disk, has usually been carried out by magnetizing its magnetic layer in the direction of its surface and utilizing the residual magnetization thereof. This way of magnetic recording has, however, a drawback. As a higher recording density is attained by recording signals having a shorter wavelength, an increase of diamagnetism in the recording medium causes a reduction of residual magnetic flux density and thereby results in the failure of the medium to exhibit a satisfactory output for reproduction.
A great deal of research and development work has, therefore, been accomplished to obtain a practically useful magnetic head of the perpendicular recording type which can magnetize the magnetic layer of a recording medium in the direction of its thickness to reduce diamagnetism when recording signals having a short wavelength to achieve an improved recording density. While a variety of constructions have been proposed for this type of magnetic head, a single-pole head of the one-sided access type is the most suitable type from a standpoint of practical use.
The recent requirements for a higher recording density and a shorter access time have, however, created a demand for a smaller and lighter magnetic head. Attention has, therefore, come to be drawn to a thin-film head of the perpendicular magnetic recording type.
A known thin-film perpendicular magnetic recording and reproducing head is constructed as shown by way of example in FIGS. 5a and 5b of the accompanying drawings. FIG. 5a is a front elevation of the transducer portion of the head which faces a recording medium 30, and FIG. 5b is a vertical section thereof. The head comprises a magnetic member 1 formed from, e.g. soft ferrite, a non-magnetic material 3 laid on it and defining a gap layer, a thin-film conductor coil 4 on the non-magnetic material 3, an insulating layer 5 covering the coil 4, a thick-film magnetic layer 7 formed on the insulating layer 5 from, e.g. a Permalloy, Sendust, or amorphous cobalt alloy, a main pole film 8 formed on the layer 7 which prevents the magnetic saturation of the film 8 during recording, and a protective film 9 formed on the film 8 for protecting the head.
The main pole film having a very small thickness has its end portion exposed in the end surface of the head, facing the recording medium, as shown in FIGS. 5a and 5b, and a magnetic flux is, therefore, concentrated on the exposed end of the main pole film, so that the recording of signals is effected by a strong magnetic interaction which occurs between the exposed end of the main pole film and the magnetic layer of the recording medium facing it. The perpendicular magnetic recording type of head can, therefore, achieve a higher recording density than what can be achieved by the older type of head which magnetizes the magnetic layer of the recording medium longitudinally along its surface. The thin-film head has, however, been found to present a serious problem which is due to the very small thickness of its main pole film. It is so easily affected by an external magnetic field which is slightly produced by, e.g., a spindle, or head driving motor, that its output for reproduction is greatly lowered, or even disappears.
Attempts have, therefore, been made to shield the source of any such external magnetic field. Those attempts have, however, been found not only to add to the complexity of apparatus design, but also to be unable to eliminate the influence of any such magnetic field completely. As a consequence, it has been very difficult to obtain a reliable recording and reproducing head.
A solution to this problem has been proposed by, for example, the Japanese patent application laid open to the public under No. 129909/1987 or 129926/1987. It is a magnetic head of the type in which a head chip comprising a main magnetic pole and an auxiliary magnetic pole, as hereinabove described, is mounted within a concavity formed in a magnetic material block serving as a magnetic shield. This type of head has, however, been found difficult to make sufficiently small and light in weight to be a thin-film head. Moreover, its special construction has been found to imposed a great restriction on the shape in which it can be made.